Leaf minimum conductance dynamics during and after heat stress: Implications for plant survival under hotter droughts

Exposure to temperatures above a critical threshold (temperature of phase transition, Tp) can damage the leaf cuticle, leading to increased leaf minimum conductance (gleaf-res). Despite the implications of increased gleaf-res for species survival under hotter-drought conditions, little is known about the dynamics of gleaf-res variation after heatwave episodes. Here, we examined the gleaf-res variation before, during, and after exposure to high temperatures (HTs) in a group of representative Cerrado tree species. Through multiple experiments, we compared gleaf-res in leaves previously exposed to different temperatures for varying durations with leaves not submitted to HT. Leaves previously exposed to temperatures above Tp and subsequently cooled had higher gleaf-res measured at 25 °C than leaves not exposed to HT, suggesting a "thermal leaky legacy" effect that negatively impacted plant survival under contrasting simulated drought scenarios. This legacy effect was induced by short periods of heat stress and increased proportionally with rising temperatures. Notably, increased gleaf-res was observed even after 24 h of leaf storage, evidencing that thermal-induced damages to the leaf cuticle cannot be fully repaired within a daily cycle. Overall, our study highlights the threats that increased gleaf-res during and after heatwaves may pose to plant performance and survival under drought conditions and emphasizes the importance of considering the dynamic nature of such water leaks to improve the predictions of drought-induced mortality events in a warmer and drier world.